A condition monitoring system is used for monitoring the condition of process equipment and parts thereof. In the system, signals from objects to be monitored are normally measured by various sensors and, for example, frequency spectra and various indices are computed from them to indicate the condition of the object to be monitored.
Objects to be monitored typically include rotating shafts of various machines, bearings, or other rotating parts, such as cogged wheels of a gearbox, or turbine rotors, as well as various revolving objects in devices. Objects to be monitored also include, for example, rolls, pumps, blowers, screens, grinders, barking drums, mixers, wires, and felts in the manufacturing process of paper and pulp. The objects are typically subjected to friction, which causes wearing and faults that can lead to a breakdown of the machine or the object monitored. For measurements, vibration sensors attached to the object to be monitored are typically used to measure the vibration as acceleration, speed, or offset. Pressure sensors are also used in monitoring pumps, screens and hydraulics for measuring pressure pulsations occurring in a pipework.
Typically, the monitoring is performed by measuring a signal of a given length at regular intervals and by computing the required indices from each measured signal. For example, it is possible to measure a signal of ten seconds once an hour from each object to be monitored. For the values to be computed, certain limit values can be defined for giving an alarm if these limits are exceeded so that a component that is about to fail can be replaced with a new one during the next stoppage before the actual failure in the object to be monitored causes greater damage or extra downtime.
The actual process comprising the objects to be monitored is typically controlled by means of an automation system. In general, a so-called distributed control system (DCS) is used, which typically comprises several process stations, I/O devices and monitoring stations, at least one system bus, programming devices, a database server, and a user interface. The process stations are normally located in the vicinity of the process. The process stations comprise I/O units (input/output), which receive and process measuring signals transmitted by sensors installed for the surveillance of the process. The I/O units can also be placed close to the objects to be measured, apart from the process stations. Communication between the distributed I/O unit and the process station takes place via an I/O bus. The process stations take care of the processing of the measurement data, the computation of the controls and the generating of the controls in situ. Thus, the measurement data are not transmitted to a central computer for computation and returning of the control values.
These two systems described above, the condition monitoring system and the automation system, typically operate independently of each other. Results obtained in the condition monitoring system can be transmitted to the automation system, whereby the automation system can transmit control instructions to the process, for example stop a device in a damage situation.
FIG. 1 shows a system of automation and condition monitoring according to prior art. The system comprises an automation system and a condition monitoring system 11, which are independent of each other.
In the automation system 1, at least one sensor 3 is coupled to different components or devices 2 in the process to collect signals indicating the condition of the process, that is, measurement data required for controlling the process. The signals measured from each sensor are led into at least one I/O unit 4 comprising at least one I/O module 33. The I/O module typically contains at least one electronics card and the other components required for forming the I/O (inputs and outputs). The sensors 3 may measure, for example, the pressure or the temperature prevailing in the process or process components 2, the rotational speed of moving parts, the properties of a product to be manufactured, or the flow rate or level of suspensions flowing in the process. For example, in the case of a paper manufacturing process, it is possible to measure, among other things, variables relating to the manufacture and finishing of paper pulp or a paper web. These include, among other things, the variables relating to the beating or digestion of pulp, the variables relating to the running of the paper machine, as well as the variables relating to the quality of paper to be manufactured, such as moisture, grammage, formation, or other properties. The I/O unit 4 receives measurement signals and, among other things, converts the analog signals to digital format. From the I/O unit 4, the signals are transmitted via an I/O bus 5 to a process station 6. The process station 6 comprises process station software, by means of which various indices and functions are computed from the measurement signals. The computation and generation of the controls also takes place in the process station. From the process station 6, the digital signals and/or the computed indices or functions are transmitted in the form of data to be stored in a database server 7. The real-time data obtained from the process station and the history data obtained from the database can be viewed in a user interface 8.
The process station 6 is coupled to a communication bus 9, normally an Ethernet network. If there are more than one process station 6 in the system, they can all be connected to the same communication bus 9. The user interface 8 is coupled to a separate communication bus 10. The database server 7 is coupled to both communication buses 9 and 10, and it communicates with both the process station and the user interface. The communication buses can also be formed by coupling the process station 6, the database server 7, as well as the user interface 8 to one and the same communication bus.
The condition monitoring system 11 also comprises at least one sensor 13 for collecting signals indicating the condition of devices 12. The sensors may be sensors for measuring the acceleration, speed or offset of vibration, or the temperature, the pressure, the flow rate, or the rotational speed. The signals measured from each sensor are led into an I/O unit 14 comprising at least one I/O module. The I/O module typically comprises at least one electronics card and the other components required for forming the I/O. The components forming the I/O module may be arranged within the same housing. The measurement signals transmitted by the sensors installed for the surveillance of the process are processed in the I/O unit. Among other things, the I/O units convert the analog signals into digital format. The analog measurement signal is obtained from the measurement sensor, which is, for example, a piezoelectronic acceleration sensor. However, the measurement signal may also be digital, wherein the I/O module receives a ready sampled condition monitoring signal from the digital sensor and transmits it to the communication bus of the I/O unit. The digital sensors may transmit the signal to the I/O module by means of a cable or wireless data transfer medium. The I/O module may also perform modification of the signal by pre-processing the sampled signal in digital format before transmitting it to the I/O bus. Typical signal modification operations include digital filtering and the conversion of the signal sampling frequency by resampling.
From the I/O unit, the signals are transmitted via an I/O bus 15 to a process station 16 in the condition monitoring system. The process station 16 comprises process station software, by means of which various indices and functions are computed from the measurement signals. Typical operations of digital signal processing include, for example, linear or non-linear scaling, digital filtering, conversion of the signal sampling frequency by resampling, and fast Fourier transform (FFT). From the process station 16, the digital signals and/or the computed indices or functions are transmitted in the form of data to be stored in a database server 17. The real-time data obtained from the process station and the history data obtained from the database can be viewed in a user interface 18. The number of process stations and user interfaces shown in the figure is only one, but there may be several of them, depending on the size of the installation.
Typically, the process station 16 is coupled to a separate communication bus 19, normally an Ethernet network. If the number of process stations 16 in the system is greater than one, they can all be connected to the same communication bus 19. The user interface 18, or user interfaces if the number of user interfaces is greater than one, is/are coupled to a separate communication bus 20. The database server 17 is coupled to both communication buses 19 and 20, and it communicates with both the process station and the user interface. It may also be used as a router between them. Also in the condition monitoring system, the communication buses can be arranged so that the process station 16, the database server 17, as well as the user interface 18 are coupled to one and the same communication bus.
For transmitting the condition monitoring data from the condition monitoring system 11 to the automation system 1, communication servers are connected to both systems, for example OPC servers, which are capable of transmitting data between the systems. The first communication server 21 is connected to the automation system. The second communication server 22 is connected to the condition monitoring system 11. The servers 21 and 22 are connected to each other by means of a wire 23. It is also possible to transmit data between the communication servers 21 and 22 by means of wireless communication. In this case, the servers 21 and 22 comprise means for wireless communication.
Furthermore, both systems comprise separate planning units with tools and software for configuring the systems. The automation system 1 comprises a planning unit 24, and the condition monitoring system 11 comprises a planning unit 25.
As already stated above, the condition monitoring system and the automation system typically operate independently of each other. The reason for this is the fact that the automation system is not capable of operating in the dynamic range required by the condition monitoring system, which prevents the processing of condition monitoring signals directly in the automation system.
As presented above, the I/O means of the automation system consist of I/O modules and I/O buses which transmit signals from the I/O modules to the process station. Measurements are taken continually, at regular intervals. The I/O buses presently used in automation systems are not capable of transmitting large numbers of signals fast forward, but a typical I/O sampling frequency is 50 Hz. This sampling frequency is insufficient for condition monitoring applications.
The condition monitoring system also comprises I/O means consisting of I/O modules and I/O buses. For monitoring the mechanical condition of machines, vibration measurements are typically used, whose signal band ranges, for example, up to 10 kHz. For this reason, the sampling frequency of vibration signals is 2 to 3 decades greater than in the automation system. For example, a signal band of 10 kHz will require a sampling frequency of at least 20 kHz; in other words, the sampling interval is 0.05 ms. Due to the high sampling frequency, the amount of data produced by the I/O modules also increases to a corresponding extent. Conventionally, the I/O buses used in automation systems are not designed to transfer such an amount of data forward, but it has been necessary to process the condition monitoring signals in a separate system.
A problem in the use of separate automation and condition monitoring systems is that these systems do not communicate with each other without separate measures. For communication, a link must be separately built up and configured for transmitting data from one system to the other. The measurement data on vibration signals and/or the computation results based on them can be transmitted, as described above, by means of various communication interfaces from the condition monitoring system to the automation system. Furthermore, a separate communication interface is required between these two systems. The communication interface is, for example, the OPC protocol and the hardware and software components required by it.
The transmission of data between the two systems is slow by applying methods of prior art. It is slow to take measures that require fast, real-time control operations, such as to implement operations for protecting the process and its parts, for example to stop the apparatus in damage situations. Another problem is caused by communication breakdowns between the two systems.
The use of smart field devices has been proposed as a solution to the above-mentioned problems. Such a solution is presented, for example, in US publication 2005/0072239. It presents a vibration monitoring system, in which a smart vibration sensor is installed in an object to be monitored. This means that a transmitter is installed in connection with the vibration sensor, comprising not only software and algorithms relating to the transmission of signals but also software relating to the processing and diagnostics of signals, capable of estimating and anticipating faults to evolve in the object. When the measurements indicate that the object that is measured is becoming faulty, the smart vibration sensor transmits this information to the control means controlling the process. Field buses are used for communication. This solution, too, comprises two separate systems: a smart vibration sensor to take care of the condition monitoring, and a separate automation and control system to take care of the controls of the process. Consequently, the system is subjected to the same problems as were described above. Furthermore, the use of field buses poses a substantial limitation on the quantity of data to be transmitted. For example, a signal sample obtained from a vibration sensor typically contains thousands or tens of thousands of sample points. In practice, the capacity of the bus poses a substantial limit on the possibility to transfer such data quantities to the user interface for a more detailed analysis.
Publication WO 01/42863 discloses a method of prior art for monitoring the condition of process components by utilizing a condition monitoring system and a control system which are independent of each other. In the method, acoustic signals caused by vibrations are measured. The measured signals are led to a signal monitoring block. The process is controlled by a control system that is independent of the condition monitoring and comprises an operation and observation block and a control block. The communication between the signal monitoring block that processes the condition monitoring signals, the operation and observation block and the control block of the control system is guaranteed by OPC protocols. Thus, the operation and control system and the condition monitoring system are separate systems, even though they are installed in the same computer. A separate communication interface with software components is still needed between the different systems.